Saccadic Reaction Times in Infants and Adults: Spatiotemporal Factors, Gender, and Interlaboratory Variation

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Abstract

Saccade latency is widely used across infant psychology to investigate infants’ understanding of events. Interpreting particular latency values requires knowledge of standard saccadic RTs, but there is no consensus as to typical values. This study provides standard estimates of infants’ (n = 194, ages 9 to 15 months) saccadic RTs under a range of different spatiotemporal conditions. To investigate the reliability of such standard estimates, data is collected at 4 laboratories in 3 countries. Results indicate that reactions to the appearance of a new object are much faster than reactions to the deflection of a currently fixated moving object; upward saccades are slower than downward or horizontal saccades; reactions to more peripheral stimuli are much slower; and this slowdown is greater for boys than girls. There was little decrease in saccadic RTs between 9 and 15 months, indicating that the period of slow development which is protracted into adolescence begins in late infancy. Except for appearance and deflection differences, infant effects were weak or absent in adults (n = 40). Latency estimates and spatiotemporal effects on latency were generally consistent across laboratories, but a number of lab differences in factors such as individual variation were found. Some but not all differences were attributed to minor procedural differences, highlighting the importance of replication. Confidence intervals (95%) for infants’ median reaction latencies for appearance stimuli were 242 to 250 ms and for deflection stimuli 350 to 367 ms.

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